1. Field of the Invention
The present invention relates to a method of manufacturing a wiring circuit board formed with a solder resist layer.
2. Description of the Related Art
It has been conventional practice to provide a heat-resistant material known as a solder resist in a required portion of a wiring circuit board, on which electronic components are to be mounted, by using a screen printing technique and an exposure and development technique to provide a solder resist layer on a conductor pattern of the wiring circuit board.
A material for the formation of such a solder resist layer generally incorporates additives such as a flame retardant and a pigment, in addition to a polymeric material serving as a main ingredient. The use of these additives imparts a characteristic of flame retardancy to the solder resist layer. In recent years, it has been proposed to use as a resist material, for example, a photosensitive resin composition incorporating, a cyclic phosphazene compound serving as the above-mentioned flame retardant, without using halogen flame retardants, for the formation of the solder resist layer from the viewpoint of environmental issues (as disclosed, for example, in Japanese Patent Application Laid-Open No. 2005-266494).
There has, however, arisen such a problem that when a wiring circuit board formed with a solder resist layer employing the above-mentioned photosensitive resin composition is used or left standing in a high-temperature and high-humidity atmosphere, various additives contained in the solder resist layer separate out, which results in contamination of a product. In particular, the above-mentioned cyclic phosphazene compound tends to easily separate out, thereby becoming a problem. In the manufacture of the wiring circuit board, on the other hand, it has been a common practice to carry out an inspection step to thereby remove contaminants and the like remaining on the surface of the wiring circuit board by using a material impregnated with an organic solvent such as ethanol. However, there has been another problem, that is, the solder resist layer dissolves into the organic solvent such as ethanol it the curing of the solder resist layer is insufficient.